This invention relates to liquid ring gas pumps, and more particularly to liquid ring gas pumps with ports for admitting and emitting gas at an axial end of the rotor in the pump.
Liquid ring gas pumps with ports at an axial end of the rotor are well known as shown, for example, by the first several Figures in Dardis et al. U.S. Pat. No. 5,213,479. In many of these pumps the rotor is mounted on a cantilevered drive shaft. This means that the drive shaft has bearings adjacent only one axial end of the rotor. The shaft does not extend beyond the other axial end of the rotor to a second bearing adjacent that other axial end. Instead, the rotor is typically secured to the cantilevered end of the shaft via any of several types of fasteners such as a nut threaded on the end of the shaft, a bolt threaded into the end of the shaft, etc. The fastener may be recessed in the adjacent end of the rotor (e.g., to keep the cantilevered shaft as short as possible, to keep the fastener away from the port structure (described below) in order to help simplify the port structure, etc.).
Adjacent the axial end of the rotor that does not have an adjacent shaft bearing, pumps of the type described above typically have a port structure. The port structure generally has at least one gas inlet port and one gas outlet port. Each of these ports is radially spaced from the longitudinal axis of the rotor drive shaft (which longitudinal axis may have to be extended from the actual end of the shaft to reach the port structure). In addition, these ports are spaced from one another in the circumferential direction around the above-mentioned longitudinal axis. The gas inlet port is used to admit gas at a relatively low pressure to the working spaces of the pump, which are between circumferentially spaced, radially outwardly and axially extending blades of the rotor. As the rotor rotates, it conveys the gas it receives from the inlet port to the circumferential location of the outlet port. In the process of conveying the gas in this manner, the rotor also compresses the gas being conveyed. This is done in cooperation with a quantity of liquid (typically water) maintained in the pump. The rotor blades engage this liquid and form it into a recirculating ring which provides the radially outer boundary of the working spaces of the pump. The liquid ring is somewhat eccentric to the rotor so that the size of each working space changes as that working space moves around the rotor axis. This change in working space size is used to compress gas in the pump. When the gas has been compressed and conveyed to the outlet port, it exits from the rotor via the outlet port.
In the typical pump of the type described above the axial end of the rotor which is adjacent to the port structure is substantially planar. Of course, the working spaces of the pump open through this rotor axial end plane, and the above-mentioned recess for the rotor fastener also opens through this plane. The adjacent axial end face of the port structure is also substantially planar and axially spaced from the rotor end plane by a relatively small, substantially planar clearance. Again, the gas inlet and outlet ports open through the port structure axial end plane, and a liquid supply port may also open through this plane to communicate with the above-mentioned recess in the rotor. Liquid (typically water, but in any event the same as the liquid used in the above-described recirculating ring) is forced into the planar clearance between the facing rotor end and port structure end planes to help prevent gas from leaking around the axial end of the rotor from high pressure to low pressure regions in the pump. This liquid is not static in this clearance, but rather flows continuously through the clearance to enter the recirculating ring.
While the above-described liquid sealing of the axial end of the rotor is effective to a significant degree, there is room for improvement in this aspect of the pump design. Moreover, the effectiveness of this rotor end sealing technique is influenced to a substantial degree by the area of the axial end of the rotor that is opposite a corresponding axial end of the port structure, especially in the annulus of rotor axial end surface that surrounds the above-mentioned rotor fastener recess. For more effective sealing it is desirable to increase the radial width of this annulus. But other considerations tend to take away from this radial width. Examples of these other considerations are a desire to keep the overall dimensions of the pump as small as possible, and a desire to make the rotor fastener recess as large as possible. A larger rotor fastener recess improves access to the recessed fastener (e.g., facilitating use of standard fasteners and standard tools which may not be optimized for slenderness). A larger rotor fastener recess may also make it possible to reduce the amount by which the drive shaft diameter has to be reduced at the fastener, thereby allowing the use of a larger fastener and avoiding weakening of the shaft at the fastener. A larger rotor fastener recess may also allow new types of fasteners to be used. For example, a collet-type fastener can be tightened around the drive shaft without the shaft being specially adapted in any way to receive the fastener. This is highly desirable because it means that the shaft can be a completely standard electric motor shaft. The motor does not have to be specially made (or subsequently modified) for this use. Also the shaft diameter is not reduced and thereby weakened in any way at the fastener.
In view of the foregoing, it is an object of this invention to improve rotor end sealing in liquid ring pumps of the type described above.
It is a more particular object of this invention to allow the radial width of the planar annulus around the rotor fastener recess in the above-described pumps to be reduced without losing rotor end sealing, and preferably even with an increase in rotor end sealing.